This invention pertains to protection and control systems for large steam turbines and in particular to a control system which is operative to protect the turbine from the effects of sudden changes in steam supply pressure.
There is, in the electrical power generating industry, a continual search for ways to generate electricity more economically and more efficiently. In the current situation of high energy consciousness, with fuel for power plants at an absolute premium, efficiency boosting techniques and methods of operation once thought to be of marginal value in view of other related problems associated with some of these methods are now being turned to to achieve even fractional increases in power output per unit of fuel (i.e., improved heat rates).
One technique that is getting increased attention in this regard is known as "sliding pressure operation." Useful with the large steam turbines commonly employed in the commercial scale generation of power, sliding pressure operation allows the turbine to be operated with the steam admission control valves substantially wide open while load changes (on the generator end of the tubine-generator set) are sustained by causing the boiler to produce more or less steam energy. This mode of operation minimizes the pressure drop across the control valves at reduced loads and therefore provides a significant improvement in heat rate under those conditions. As might be expected, however, this mode of operation requires some tradeoffs in other operating considerations.
For example, to achieve the sliding pressure operation, a proportional initial pressure regulator ordinarily used, must be deactivated. Should a sudden drop in steam pressure then occur, a rather violent reaction is produced in the boiler, causing liquid water to form in the steam. This can be carried into the tubine with potentially devastating effect. This phenomenon, known as water induction, must be carefully guarded against to protect the internal components of the turbine.
It is therefore an objective of the present invention to provide means for protecting a steam turbine from the effects of water induction such as occurs with a sudden drop in steam pressure at the boiler. The invention has particular utility when applied to turbines adapted to sliding boiler pressure operation and for which the normal initial pressure regulation mechanism has been disarmed to achieve that mode of operation.